In a structure of YBa2Cu3O7-X (YBCO) superconducting wire among the oxide superconducting wire, one layer or plural layers of a biaxially-oriented thin film of the inorganic material is formed onto the metallic substrate. And a superconducting film and a stabilized layer are formed in sequence onto the biaxially-oriented thin film of the inorganic material. Because this wire has the biaxially-oriented crystal, the critical current (Ic) value is higher than the bismuth type silver sheathed wire, and the magnetic-field property is superior in the liquid nitrogen temperature. Therefore, by using this wire, it is expected that the superconducting equipment which is used in the low temperature at present can be used in the high temperature state.
The characteristic of this YBCO superconductor is affected strongly by the orientation of that crystal. Therefore, the characteristic of this YBCO superconductor is affected strongly by this substrate which constitutes the lower layer and by the orientation of the crystal of an intermediate layer.
That is, a crystal system of the YBCO superconductor is an orthorhombic crystal. Therefore, in order to bring out the characteristic of the material in conducting property, it is required that not only a CuO face of the crystal but also an in-plane crystal orientation is arranged. The reason is that a little mismatch of the orientation generates grain boundaries of the twin crystal and deteriorates the conducting property.
Various methods for the film formation of The YBCO superconducting wire are studied now. IBAD (Ion Beam Assisted Deposition) method or RABiTS (Trade Mark: Rolling Assisted Biaxially Textured Substrate) method is known as the manufacturing technology of the biaxially-oriented metal substrate that the in-plane oriented intermediate layer is formed onto the tape-shaped metal substrate. And many YBCO superconducting wires having the intermediate layer whose in-plane orientation degree and orientation are improved and which is formed onto non-oriented or oriented metal tape are reported. For example, the following rare earth-containing tape-shaped oxide superconductor is known. As the substrate, that rare earth-containing tape-shaped oxide superconductor uses the substrate which consists of Ni or Ni based alloy having oriented texture by heat treatment after strong rolling process. And the Ni oxide thin film, the oxide intermediate layer which is formed by MOD method of CeO2 and so on and the YBCO superconducting layer are formed in sequence onto the surface of this substrate (for example, refer to Patent document No. 1).
Among the background arts, the method using IBAD substrate has the best characteristic. In this method, onto the tape-shaped Ni based substrate (hastelloy etc.) having nonmagnetism and high strength, the intermediate layer (CeO2, Y2O3, YSZ etc.) or the intermediate layer of two layer structure (YSZ or Gd2Zr3O7/CeO2 or Y2O3 etc.) is formed by depositing the particles generated from the target using laser evaporation during irradiation of ion from the diagonal direction for this Ni based substrate. And these intermediate layers have high orientation and inhibit the reaction with the elements which constitute the superconductor. And after forming the CeO2 film onto that layer by PLD method, the YBCO layer is formed by PLD method. Thereby, the superconducting wire is produced (for example, refer to Patent document No. 2 to No. 4).
However, in this method, because all layers are formed by vacuum process of gas phase method, there is advantage that the dense and smooth intermediate layer film can be obtained. But there are problems that the film formation speed is slow, the equipment cost becomes high and the wire cost rises. Although some film formation methods have been studied other than this IBAD method, the available methods for solving about the problems of the cost and the formation speed have not been reported.
The most effective method to actualize the low cost is MOD method (Metal Organic Deposition Processes) which forms the oxide layer by using the metal organic acid salt or the organic metal lie compound as the raw material, and by giving the heat treatment after coating the raw material.
Although this process is simple, it is difficult to obtain the film which has the sufficient capability as the intermediate layer because of the crack occurrence by the volume decrease at the time of heat decomposition and because of the diffusion of the elements of the substrate and the imperfection of the crystal by the imperfection of crystal grain growth.
Generally, CeO2 is used as the intermediate layer of the Y type superconductor as described above. This is because the CeO2 intermediate layer is very consistent with the YBCO superconducting layer, and because the CeO2 intermediate layer is known as one of the best intermediate layer because of small reactivity for the YBCO layer. If the film of this CeO2 intermediate layer is formed by MOD method, because the cracks occur from the difference of the coefficient of linear expansion between the film and the substrate, the function of the intermediate layer cannot be achieved. If the solid solution film that Gd was added into CeO2 is formed onto the Ni based substrate by MOD method, the occurrence of the cracks can be restrained. However, the diffusion of the elements from the Ni or Ni based substrate cannot be restrained.
Besides, Zr type intermediate layer is also studied and the effect of the prevention of the element diffusion from the substrate is reported. About the wire using this Zr type intermediate layer, it is reported from some research organizations that Jc exceeding 1 MA/cm2 is obtained.
Patent document No. 1: Japanese Patent Publication No. 2004-171841
Patent document No. 2: Japanese Patent Publication No. Hei04-329867
Patent document No. 3: Japanese Patent Publication No. Hei04-331795
Patent document No. 4: Japanese Patent Publication No. 2002-202439